New Game Plus mode
Successfully complete the game under the Normal or Hard difficulty setting. This mode allows you to keep your previously earned gadgets and experience points. Also, there will not be any counter icons on thugs, thugs will be more difficult from the start, thugs will have different configurations, and Bosses will be tougher.

Harley Quinn pregnancy
Go to the manager's office inside the Steel Mill. On the floor, next to the Harley Quinn costume, there is a positive pregnancy test.

Easy "Story Teller" achievement or trophy
Play offline (not logged into Xbox Live or PlayStation Network as your system date is automatically set via the internet). Set the date of your console to a holiday date (for example, January 1, February 14, etc.) then load a saved game file where the story progress is past rescuing Catwoman. Enter the courthouse and talk to Calendar Man in the basement. He will tell you a story about the current month's holiday and tell you to return for the next month. Save the game by leaving the building. Exit to the system settings, then manually change the date to the next holiday. Repeat the process until you have cycled through the entire calendar year. The calendar on the wall next to his cell will highlight the holiday dates for the current year and scribble out which months you have already spoken to Calendar Man about.